Self-calibrating magnetic field monitor

ABSTRACT

A self-calibrating magnetic field monitor is disclosed. In one embodiment, a magnetic field sensor repeatedly generates an electronic signal related to the magnetic field. In addition, a calibration module generates a relative baseline signal based on an average value of the electronic signals for a given time period. A comparator compares the electronic signal with the relative baseline signal and generating an output signal if a difference in the comparing is greater than or equal to a threshold.

CROSS REFERENCE TO RELATED APPLICATIONS

The present patent application is a continuation of U.S. patentapplication Ser. No. 13/368,219, filed Feb. 7, 2012, entitled“Self-Calibrating Magnetic Field Monitor,” by Cory J. Stephanson et al.,assigned to the assignee of the present application which isincorporated in its entirety herein; which is a continuation of U.S.patent application Ser. No. 12/431,418, filed Apr. 28, 2009, entitled“Self-Calibrating Magnetic Field Monitor,” by Cory J. Stephanson et al.,assigned to the assignee of the present application which isincorporated in its entirety herein; which claims priority to the U.S.Provisional Patent Application No. 61/049,437 entitled “CommunicationsOperational Bridge and Rapid Assessment Sensor Cued Imaging” by Cory J.Stephanson et al., filed May 1, 2008; which is incorporated by referencein its entirety herein.

TECHNICAL FIELD

The field of the present invention relates to a magnetic field monitor.

BACKGROUND

Metal detectors are used in many different applications. For example,present security systems use metal detectors to detect ferrous metal ona person or within closed bags. Other types of magnetic field monitorsinclude large magnetic field sensors that monitor magnetic fieldstrengths from locations such as satellites and the like.

Metal detectors may be a large, heavy, highly calibrated walk throughdevice or a smaller hand-held metal detector or “wand”. Usually, thewalk through device is utilized to detect metallic objects within adoorway sized area through which a person or object is placed. Incontrast, a hand held device is utilized to detect metallic objects bymoving around or past an object or person.

Normally, training personnel in the operation of metal detection ormagnetic field monitoring systems and the proper methodology of using,calibrating and deploying the metal detection systems is a significantinvestment in time, training and cost. Moreover, if the systems aremiss-calibrated or improperly or incorrectly utilized, detectioncapabilities can become significantly reduced.

Thus, there is a long felt need for an improved magnetic field monitorsystem and method having simplified user interactions including set-up,maintenance and operation.

SUMMARY

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used as an aid in determining the scope of the claimed subjectmatter.

A self-calibrating magnetic field monitor is disclosed. In oneembodiment, a magnetic field sensor repeatedly generates an electronicsignal related to the magnetic field. In addition, a calibration modulegenerates a relative baseline signal based on an average value of theelectronic signals for a given time period. A comparator compares theelectronic signal with the relative baseline signal and generating anoutput signal if a difference in the comparing is greater than or equalto a threshold.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of one embodiment for monitoring a magneticfield in an environment is shown.

FIG. 2 is a block diagram of a self-calibrating magnetic field monitorshown in accordance with one embodiment of the present technology.

FIG. 3 is a flowchart of an exemplary method for monitoring a magneticfield in an environment for magnetic field fluctuations in accordancewith one embodiment of the present technology.

FIG. 4 is a plurality of graphs illustrating one embodiment formonitoring a magnetic field in an environment in accordance with oneembodiment of the present technology.

FIG. 5 is a plurality of graphs illustrating another embodiment formonitoring a magnetic field in an environment in accordance with oneembodiment of the present technology.

FIG. 6 is a diagram of an environment having a magnetic field monitortherein in accordance with one embodiment of the present technology.

FIG. 7 is a block diagram of an exemplary computer system in accordancewith one embodiment of the present technology.

The drawings referred to in this description should be understood as notbeing drawn to scale except if specifically noted.

FIG. 8 is a diagram of a corridor having a magnetic field monitor with aplurality of magnetic field sensors therein in accordance with oneembodiment of the present technology.

DETAILED DESCRIPTION

Reference will now be made in detail to embodiments of the presenttechnology, examples of which are illustrated in the accompanyingdrawings. While the technology will be described in conjunction withvarious embodiments, it will be understood that they are not intended tolimit the present technology to these embodiments. On the contrary, thepresented technology is intended to cover alternatives, modificationsand equivalents, which may be included within the spirit and scope thevarious embodiments as defined by the appended claims.

Furthermore, in the following detailed description, numerous specificdetails are set forth in order to provide a thorough understanding ofthe present technology. However, the present technology may be practicedwithout these specific details. In other instances, well known methods,procedures, components, and circuits have not been described in detailas not to unnecessarily obscure aspects of the present embodiments.

Overview

A passive, self-correcting and self-calibrating magnetic field monitorhaving sensitive long range detection characteristics is described. Inone embodiment, the magnetic field monitor has a small footprint (e.g.,the size of a matchbook) and is reliable and ruggedized. The magneticfield monitor is well suited to stand-alone operation as well asintegration with legacy/future technology.

In one embodiment, the magnetic field monitor described hereinidentifies minute changes in soft-magnetic effect without beingdeleteriously affected by the ambient earth magnetic field structure orany changes naturally occurring thereto. For example, theself-calibrating magnetic field monitor is capable of detecting atactical knife at greater than 25 meters and larger weaponry such aspistols and rifles at over 100 meters.

In general, the magnetic field monitor self-calibrates after beingintroduced into an environment of operation. The post-introductionself-calibration process allows deployment in different environmentswith minimal testing, support or set-up time. Additionally, the magneticself monitor repeatedly performs the self-calibration overpre-determined time periods such that natural changes that occur in anenvironment's magnetic field are filtered or absorbed. For example,fluctuation in the strength of the environment's magnetic field causedby changes in an environments temperature over a period of time.

In addition, the repeated self-calibration characteristics allow themagnetic field monitor to adjust to man-made changes in the environment.For example, if an armed guard approached the magnetic field monitor,the event would be detected and an output signal would be provided.However, by performing a re-calibration, magnetic field monitor is ableto re-zero based on the now different environmental magnetic fieldcharacteristics. In other words, the armed guards own metal objectswould become part of the expected magnetic field instead of an eventoutside of the normal. This self-calibrating capability also works inthe same way with other metallic objects that may already be, or areadded to the environment. Objects such as cars, other armed personnel,and the like.

Monitored Environment

With reference to FIG. 1, a block diagram 100 of one embodiment formonitoring a magnetic field in an environment is shown. In oneembodiment, FIG. 1 includes a magnetic field 110 for an environment, amagnetic field monitor 260 and an output signal 250. In one embodiment,system 100 also includes an optional accelerometer 225.

In general, an environment may be natural or built and is usuallydescribed utilizing a combination of atmosphere, climate and weatherconditions. Example, environments may include, but are not limited to,desert, tundra, canopy, jungle, riverine, aquatic, littoral, savannah,marine, urban or the like.

In one embodiment, the environment and associated magnetic field 110 ofthe environment is a localized area or portion of an environment,similar to an ecosystem. For example, the area of the environmentrepresented by magnetic field 110 may approximate the range of operationof magnetic field monitor 260.

In one embodiment, the environment and associated magnetic field 110 maybe an outdoor area. However, in another embodiment, the environment andassociated magnetic field 110 may be an indoor area such as a room, astructure or the like. In yet another embodiment, the environment andassociated magnetic field 110 may be a combination of indoor and outdoorareas such as an outpost, or the like. Additionally, part or all of theenvironment and associated magnetic field 110 may be dry, partially orcompletely submerged, partially or completely buried, and the like.

Usually, an environment will have certain magnetic field 110 strengthfor any given period of time. The strength of magnetic field 110 may berepresented in the SI units of teslas (T), webers per square meter(Wb/m²) or volt seconds per square meter (V s/m²). Moreover, differentenvironments are known to have different magnetic field 110 strengths.For example, different locations on the Earth's surface can havemagnetic field 110 strengths that range from less than 30 microteslas(μT) to more than 60 μT.

However, the strength of a specific environment's magnetic field 110will also change over time due to changes in temperature, humidity,weather conditions and the like. For example, electric currents inducedin the ionosphere near where the atmosphere is closest to the Sun havebeen known to cause daily alterations in an environments magnetic field110.

Additionally, there may be other events that change the strength of anenvironment's magnetic field 110. Events that are not related to naturalchanges. These events may include an introduction or removal of metal tomagnetic field 110. Example events include, but are not limited to, avehicle, a gun, knife, key, pen, or the like entering into or departingfrom an environment.

Generally, natural changes in magnetic field 110 occur over a relativelylonger period of time than event induced changes. For example, a changein magnetic field 110 due to temperature change will normally occur overa period of a few hours. In contrast, a person walking with a knifethrough magnetic field 110 may cause the same level of change inmagnetic field 110, but the change will occur over a period of seconds.

Magnetic field monitor 260 monitors magnetic field 110 to recognize anevent. When magnetic field monitor 260 identifies a change in magneticfield 110 due to an event, output signal 250 is generated. In oneembodiment, magnetic field monitor 260 utilizes a relative changemethodology instead of explicit field strength values when monitormagnetic field 110.

Magnetic Field Monitor

With reference now to FIG. 2, a block diagram 200 of a magnetic fieldmonitoring system is shown in accordance with one embodiment. In oneembodiment, magnetic field monitor 260 includes magnetic field sensor220, calibration module 240, and instant comparator 210. In oneembodiment, magnetic field monitor 260 also includes an optional blockcomparator 230 and accelerometer 225.

Magnetic field sensor 220 may be a flux gate magnetometer sensor, asuper conducting quantitative interference detector (SQUID), a magnetoresistive sensor, spin electron relaxation frame (SERF) sensor or thelike.

In another embodiment, magnetic field sensor 220 may comprise a strip ofmetal, thin film or the like that is sensitive to magnetic fields. Whenvoltage is applied, magnetic field sensor 220 will provide an analogsignal 130 such as a voltage, representative of magnetic field 110. Forexample, a change in magnetic field 110 will cause a change in thevoltage of signal 130. In one embodiment, signal 130 is a relative valuefor magnetic field 110 and not an explicit magnetic field strengthvalue.

Magnetic field sensor 220 samples magnetic field 110 periodically at apre-defined rate of time and generates a corresponding signal 130 foreach sampling period. For example, magnetic field sensor 220 may use a 1MHz crystal to establish a nanosecond sample rate. Magnetic field sensor220 outputs signal 130 to instant comparator 210, calibration module 240and optional block comparator 230.

Calibration module 240 receives signal 130 from magnetic field sensor220 and generates a relative baseline signal 280. For example, aftercalibration module 240 receives an initial time periods worth of signals130, calibration module 240 will average the signals 130 and generate arelative baseline signal 280. In other words, relative baseline signal280 is similar to a calibration, recalibration, zero or baseline for theparticular magnetic field 110 being monitored. In one embodiment,relative baseline signal 280 is a relative value and not an explicitmagnetic field strength value.

In one embodiment, calibration module 240 will generate a new relativebaseline signal 280 at a consistent interval. For example, a newrelative baseline signal 280 may be generated every few minutes, fewseconds, few hours or the like. By adjusting the time of generation forrelative baseline signal 280, both sensitivity and range of magneticfield monitor 260 may be adjusted. In one embodiment, calibration module240 may also include a manual option to allow a user to generate a newrelative baseline signal 280.

Calibration module 240 provides relative baseline signal 280 to instantcomparator 210 and optional block comparator 230.

Referring still to FIG. 2, in one embodiment, instant comparator 210performs a comparison between signal 130 and relative baseline signal280 to recognize a change in magnetic field 110. When the resultantdifference between magnetic field 110 and relative baseline signal 280is greater than or equal to a pre-defined difference threshold, instantcomparator 210 provides an output signal 250.

In one embodiment, instant comparator 210 does not utilize an actualmagnet field strength value as the threshold value but instead utilizesa threshold value related to the difference between signal 130 andrelative baseline signal 280. Thus, in one embodiment, neither signal130 nor relative baseline signal 280 need include a specific orquantified value for magnetic field 110 as long as magnetic field sensor220 provides a consistent representation of magnetic field 110 in signal130. However, in another embodiment, signal 130 and/or relative baselinesignal 280 may include a specified value related to magnetic field 110.

For example, the threshold value is based on the absolute value of thedifference between signal 130 and relative baseline signal 280. Byutilizing the absolute value of the difference, instant comparator 210is well suited to recognizing changes in magnetic field 110 thatincrease the field strength as well as changes in magnetic field 110that reduce the field strength.

Optional block comparator 230 operates in a manner similar to instantcomparator 210, but may be calibrated to recognize changes in magneticfield 110 over a greater time period than instant comparator 210. Whenthe change over time for relative baseline signal 280 is greater than orequal to a pre-defined threshold, block comparator 230 provides anoutput signal 250.

In another embodiment, block comparator 230 may monitor a plurality ofrelative baseline signals 280 over time to detect changes in magneticfield 110 over time. In yet another embodiment, block comparator 230does not utilize a difference between the pluralities of relativebaseline signals 280 as the threshold. Instead, block comparator 230utilizes a threshold value related to the area under the curve definedby the plurality of relative baseline signals 280. However, thefunctions described herein as being performed by optional blockcomparator 230 may be performed by either or both of instant comparator210 and calibration module 240. However, for purposes of clarity,optional block comparator 230 is described herein as separate frominstant comparator 210 and calibration module 240.

Optional accelerometer 225 is utilized to provide motion and orientationinformation to magnetic field monitor 260. For example, if magneticfield monitor were hanging from a tree, rolled across the ground,bumped, rotated, moved or the like, accelerometer 225 would provideorientation and motion information that would allow magnetic fieldmonitor 260 to maintain its calibration.

For example, if magnetic field monitor 260 is rotating accelerometer 225will provide calibration module 240 with real time information about theorientation of magnetic field sensor 220. This information allowscalibration module 240 to generate and maintain a plurality of distinctbaseline signals 280 directly related to the orientation of magneticfield sensor 220 at the time signal 130 was generated (or received).Thus, calibration module 240 is able to provide both instant comparator210 and block comparator 230 with the appropriate relative baselinesignal 280 for each signal 130 received from magnetic field sensor 220.Thus, in one embodiment, any changes in orientation of magnetic fieldmonitor 260 would be resolved at calibration module 240 prior to theoperations of either instant comparator 210 or block comparator 230.

In one embodiment, accelerometer 225 is a component found outside ofmagnetic field monitor 260. However, in another embodiment, such asshown in FIG. 2, accelerometer 225 may be located within magnetic fieldmonitor 260.

Operation

With reference now to FIG. 3, a flowchart 300 of one method formonitoring a magnetic field in an environment is shown in accordancewith one embodiment. In the following description, graphs 410-440 ofFIG. 4 and graphs 510-540 of FIG. 5 are utilized to illustrate two ofthe plurality of possible embodiments for representing a method formonitoring a magnetic field in an environment in accordance with oneembodiment of the present technology.

At 302 of FIG. 3 as well as graph 410 of FIG. 4 and 510 of FIG. 5, oneembodiment repeatedly generates a signal 130 representing magnetic field110. In one embodiment, a clock is utilized to determine when signal 130is generated. For example, a 1 MHz clock may be used such that a newsignal 130 is generated each nanosecond. In one embodiment, signal 130may be an analog signal. In one embodiment, the line plotted on graphs410 and 510 illustrates a plurality of signals 130 for a time periodA-H.

With reference now to 304 of FIG. 3 as well as graph 420 of FIG. 4 and520 of FIG. 5, one embodiment generates a relative baseline signal 280based on an average value of the signal 130. In other words, calibrationmodule 240 receives a number of electronic signals 130 from magneticfield sensor 220 over a given period of time and averages the signals130 for that time period to generate a relative baseline signal 280. Inone embodiment, calibration module 240 provides the relative baselinesignal 280 to instant comparator 210 and block comparator 230.

For example, calibration module 240 may average signals 130 over a 5second time period when generating relative baseline signal 280. Inanother embodiment, calibration module 240 may average received signals130 over a 5 minute, 20 minute, 1 hour, 2 hour, 6 hour, 12 hour, 24hour, etc. time period before generating relative baseline signal 280.In one embodiment, the length of time represented by relative baselinesignal 280 may be directly related to the sensitivity and/or range ofmagnetic field monitor 260.

With respect to FIGS. 4 and 5, time segments A-H represent the timeperiod for which relative baseline signal 280 is an average. Forexample, if calibration module 240 average signals 130 over a 20 secondtime period when generating relative baseline signal 280, then timesegment A, and similarly time segments B-H would represent 20 seconds.As shown in graph 420, in one embodiment, relative baseline signal 280is an average of the previous time periods worth of signals 130. Forexample, at graphs 420 and 520 time period A is an initial calibrationperiod and therefore has no relative baseline signal 280.

With reference now to 306 of FIG. 3 as well as graph 430 of FIG. 4 and530 of FIG. 5, one embodiment compares each signal 130 with relativebaseline signal 280. For example, as shown in graph 430 and 530, in oneembodiment, instant comparator 210 looks at the difference betweensignal 130 and relative baseline signal 280. In one embodiment, thesensitivity of instant comparator 210 is not affected by the directionof a change in strength of magnetic field 110. For example, an eventsuch as a metal object leaving the magnetic field 110 would provide achange in the strength of magnetic field 110 that would be asrecognizable as an event such as a metal object entering magnetic field110.

By utilizing a difference comparison between the consistently updatedrelative baseline signal 280 and signal 130, most changes that occurnaturally in magnetic field 110 can be dealt with prior to detrimentallyaffecting the sensitivity of instant comparator 210. For example, ifmagnetic field 110 varies naturally over time, such as can occur duringchanges in the daily temperature, Sun activity, atmospheric conditionsand the like, adjusting relative baseline signal 280 to remove thenatural magnetic field 110 variation will allow instant comparator 210to remain at a consistent and very high level of sensitivity. In oneembodiment, the operational sensitivity of instant comparator 210 may beless than or equal to the natural variations in the environment'smagnetic field 110. Therefore, by normalizing or adjusting the relativebaseline signal 280, magnetic field monitor 260 is capable of detectingfemto-Tesla signatures, e.g., signatures that are far below the Earth'sfield.

For example, as shown in graphs 410 magnetic field 110 is naturallygrowing stronger. However, the normal baseline as shown in graph 430adjusts to zero out the natural change while the event detectionthreshold 435, in either direction, remains a constant distance from thebaseline. Similarly, if the magnetic field was reduced in strength, thebaseline would be adjusted to zero out the natural change while theevent detection threshold 435 would remain a constant distance from thenormal baseline.

As shown in graph 430, in one threshold breaching event 433, such as aknife being introduced into the environment, the increase in thestrength of magnetic field 110 causes a similar change in signal 130above threshold 435. Thus, at time F, an event 433 is recognized byinstant comparator 210. Similarly, in another threshold breaching event,such as a gun being removed from the environment, the reduction in thestrength of magnetic field 110 causes a similar change in signal 130recognized as an event by instant comparator 210. As previously statedherein, in one embodiment, due to the normalization characteristics therecognized change in the magnetic field 110 may be at the femto-Teslalevel.

However, in one embodiment as shown in graphs 510 through 540 of FIG. 5,when relative baseline signal 280 is updated often, a slower event, suchas a person with a knife crawling or moving slowly through theenvironment may also become averaged out and thus not be recognized byinstant comparator 210.

One method for dealing with slower event detection would be to updaterelative baseline signal 280 less often. In so doing, slower events suchas a person with a handgun crawling or moving slowly through anenvironment would be recognized at instant comparator 210. However, theslower updates would similarly cause a reduction in the sensitivity ofinstant comparator 210.

In one embodiment, the utilization of optional block comparator 230 aswell as instant comparator 210 allows magnetic field monitor 260 tomaintain numerous levels of sensitivity to changes in magnetic field 110at the same time. For example, as shown in graphs 510-540, a slow movingevent occurred. At graph 530, the event has been averaged out due to thefaster update of relative baseline signal 280.

However, as shown in graph 540, by monitoring changes to relativebaseline signal 280, e.g., monitoring magnetic field 110 changes over alonger period of time, block comparator 230 is able to recognize event543. Thus, by utilizing both instant comparator 210 and block comparator230, magnetic field monitor 260 can have both a high level ofsensitivity as well as a large field of range.

In another embodiment, block comparator 230 may similarly compare signal130 with relative baseline signal 280 as instant comparator 210 with thedifference being block comparator 230 may use the same relative baselinesignal 280 for two or more time periods. In other words, instead ofusing the new relative baseline signal 280 each time it is provided,block comparator 230 may only utilize every other, third, etc., relativebaseline signal 280.

In another embodiment, block comparator 230 may only look at relativebaseline signals 280 and utilize a threshold based on a total change inthe size of relative baseline signals 280 over a pre-determined timeperiod. For example, a relative baseline signal 280 for time period Bmay be compared with each relative base signal for the next 7 timeperiods. An event would be detected if the difference passes apre-defined threshold difference value. In one embodiment, blockcomparator 230 may perform the comparison for each relative base signal280. Although 7 time periods are mentioned, any number of alternate timeperiods or time period portions may be used herein. Further, the numberof time periods may be adjustable depending on sensitivity or rangecharacteristics.

In yet another embodiment, block comparator 230 may only look atrelative baseline signals 280 and utilize an area under the curve typethreshold over a pre-determined time period. For example, as shown ingraph 540, block comparator 230 may calculate the area under the curvefor a given time period of relative baseline signals 280. Although 6time periods are shown, any number of alternate time periods or timeperiod portions may be used herein. Further, the number of time periodsmay be adjustable depending on sensitivity or range characteristics.

Referring now to 308 of FIG. 3, one embodiment generates an outputsignal 250 when a difference in the comparing is greater than athreshold. For example, if a person carried a knife into the magneticfield 110 being monitored, the correlating change in the strength ofmagnetic field 110 would be recognized by magnetic field monitor 260. Asa result magnetic field monitor 260 would provide an output signal 250such as an audible mechanical and/or visual alarm configured to be heardby a human being. In an alternative embodiment, output signal 250 may besent via a communication network to automatically notify designatedpersonnel when an event is detected.

In another embodiment, output signal 250 may be received by anotherdevice that will carry out a follow-on task. For example, output signal250 could provide a turn-on signal for one or more lights, such a lightlocated in the vicinity of the detected event. Additionally, outputsignal 250 could include a signal to generate a notification of thedetected event to a remote location. In one embodiment, output signal250 may initiate an automatic action to incapacitate an identifiedthreat. For example, as in a building having doors and windows that maybe electronically locked output signal 250 may automatically lock one ormore of the building's doors and windows.

Moreover, by utilizing the optional accelerometer 225, if magnetic fieldmonitor is moving, output signal 250 may include direction about theevent. In one embodiment, direction may include distance, bearing,velocity, relative velocity, and the like. Similarly, if magnetic fieldmonitor were remote, output signal 250 may include a message having oneor more attributes associated with the event, such as the location ofthe event, when the event was detected, contact information for certainpersons of interest or directions for the recipient of the message.

Output signal 250 may also incorporate an imaging and/or audio trigger.For example, in response to a received output signal 250, an imagingdevice, such as imaging device 825 of FIG. 8 will begin to captureimages and/or video of the monitored environment 600, or corridor 800.Similarly, in response to a received output signal 250, an audio devicemay begin to capture audio of the monitored environment 600. In oneembodiment, output signal 250 could incorporate any or all of the above.

With reference now to FIG. 6, an environment 600 in which magnetic fieldmonitor 260 and a remote communications device 650 is shown inaccordance with one embodiment. Although in FIG. 6 magnetic fieldmonitor 260 is shown as suspended from a tree it is merely one of aplurality of possible deployment options. Magnetic field monitor 260 iswell suited to placement on the ground, in a building, on an object suchas a table, partially or completely submerged, partially or completelyburied, and the like. Additionally, FIG. 6 illustrates one embodimentwherein accelerometer 225 would be useful.

In one embodiment, magnetic field monitor 260 wired or wirelesslytransmits output signal 250 to a remote communications device 650 byimplementing a communication technology selected from a group ofcommunication technologies consisting of AM, FM, PCM, GPS, RS232, RS485,USB, firewire, infrared and fiber optic communication technologies.

For example, in one embodiment magnetic field monitor 260 wirelesslytransmits the generated output signal to communications device 650. Forinstance, if an analog output signal 250 is generated, the signal couldbe transmitted using AM or FM communication technologies in which theoutput signal is modulated with a carrier signal, and thenelectromagnetically communicated to communications device 650. In oneembodiment, communications device 650 is utilized to receive themodulated output signal from magnetic field monitor 260, and theninitiate an action and/or route output signal 250 to another deviceeither wired or wirelessly. In so doing, the communication range ofmagnetic field monitor 260 and more specifically output signal 250 canbe significantly increased with little or no increase in size or powerrequirements of magnetic field monitor 260.

Magnetic field monitor 260 is capable of operation in both an attendedstate and an unattended state. For example, magnetic field monitor 260is well suited to be placed in an environment that is constantlysupervised, such as a checkpoint, chokepoint, or the like. In anotherembodiment, magnetic field monitor 260 is able to be “dropped” into anarea to act as a standalone environment monitor. For example, magneticfield monitor 260 may be placed in a location such as a closed hallway,off-limits area, front yard, driveway, room exit, building exit, parkinggarage, perimeter, and the like. In one embodiment, during operation inan unmanned operating environment, output signal 250 from magnetic fieldmonitor 260 may be communicated to a remote site, may initiate an alarm,initiate a lock-down sequence, provide an activation signal to anotherdevice, and the like.

As stated herein, magnetic field monitor 260 may be employed in desert,jungle, riverine, littoral and/or coastal regions. Furthermore, due tothe self-calibrating characteristics, magnetic field monitor 260 is alsocapable of operating under a wide range of physical conditions such as,high humidity, low humidity, extreme temperature ranges, dusty, dirty,sandy and muddy conditions, partially or completely submerged, partiallyor completely buried, and the like. For example, magnetic field monitor260 is capable of operating in environments with one or more significantphysical conditions such as, but not limited to, tropical or arcticenvironments.

Additionally, magnetic field monitor 260 is capable of operation inenvironments having changing physical conditions. That is, therepetitive self-calibrating capabilities of magnetic field monitor 260allow magnetic field monitor 260 to remain viable in a constantlychanging environment such as a desert environment that may have daily orweekly environmental changes (e.g., temperatures that range from at orbelow freezing at night to 40 degrees Celsius midday). In anotherembodiment, magnetic field monitor 260 is also well suited for operationin a controlled environment having little or no harsh physicalconditions, such as an airport terminal, building, parking lot and thelike.

In another embodiment, magnetic field monitor 260 is also very useful inan environment where a walk-through or hand-held metal detector isutilized. Although, as stated herein, magnetic field monitor 260 is wellsuited as a replacement for either or both of the walk-through andhand-held metal detector, due to the distinctly different approach ofmonitoring an environments magnetic field, magnetic field monitor 260 isalso well suited for use in conjunction with a walk-though and/orhand-held metal detector. For example, in many security environmentspeople are formed up in queue to pass through the checkpoint. Inaddition, some checkpoints such as metal-detection checkpoints provide achokepoint with many unscreened people waiting to pass through themetal-detector. The present security checkpoints do not provide securityfor people waiting to pass through. Moreover, in higher stressenvironments security personnel are on lookout for people that appearstressed or people dressed in loose clothing that are approaching thecheckpoint. In some environments, a human evaluation may be utilized bysecurity personnel prior to a suspicious person even entering thescreening queue. For example, a security guard may have to ask someoneto open up the baggy shirt or answer a few questions.

However, magnetic field monitor 260 may be deployed in this samescenario as a means of pre-scanning anyone or anything approaching thecheckpoint. For example, in one embodiment, magnetic field monitor 260may be set to trigger if an event is detected within a pre-defined areaaround the checkpoint. Such a pre-warning would allow anyone at thecheckpoint to react to the event with an amount of stand-off distance.Further, in one embodiment, when used in combination with a walk-throughmetal detector, magnetic field monitor 260 may be calibrated to increaserange while sacrificing some sensitivity since the walk-through metaldetector may be providing the finer level of sensitivity.

Although a walk-through or hand-held metal detector is utilized in theexample, it is merely as an example of one way magnetic field monitor260 may be incorporated into a previously established screeningscenario. In one embodiment, magnetic field monitor 260 may act as boththe long range and fine level detector in a similar checkpoint withoutrequiring any other type of metal detection system.

In one embodiment, two or more magnetic field sensors 220 may beutilized within a single magnetic field monitor 260. By utilizing two ormore magnetic field sensors 220, magnetic field monitor 260 would beable to determine additional information relating to an event,information such as speed, direction, velocity, etc. Moreover, one ormore of the magnetic field sensors 220 may be set for different rangeand or sensitivity detection characteristics. In so doing, a singlemagnetic field monitor 260 would be able to provide both long distancemonitoring and shorter range, but more sensitive, magnetic fieldmonitoring.

In another embodiment, two or more magnetic field monitors 260 may beutilized in a networked configuration. The networked configuration mayinclude magnetic field monitors 260 monitoring overlapping magneticfields, monitoring adjacent magnetic fields, offset magnetic fields, ora combination thereof. Further, one or more of the magnetic fieldmonitors 260 may be set for longer range detection, e.g., providinglonger distance monitoring while one or more may be set for shorterrange but more sensitive magnetic field monitoring.

For example, a first magnetic field monitor 260 may be placed in a firstlocation and a second magnetic field monitor 260 may be placed in asecond location. In one embodiment, the first and the second magneticfield monitors 260 may be monitoring overlapping magnetic fields 110. Bycomparing the electronic signals 130 from the first and second magneticfield monitors, such as at calibration module 240, common mode errorscan be detected. For example, if a similar event occurs instantly inboth magnetic fields 110 being monitored, the comparison would detectthe similar event and recognize that the event as a common error and, inone embodiment, not generate an output signal 250 for the event.

In addition, by comparing the electronic signals from two or moremagnetic field sensors, 220, increase in sensitivity and range for themonitoring of the magnetic field can be achieved. Moreover, as shown inFIG. 8, comparing the electronic signals from two or more magnetic fieldsensors, such as magnetic field sensor 220 a and magnetic field sensor220 b, allows output signal 250 to include orientation information suchas distance, speed, bearing, etc. of an event. For example, a person 805carrying a rifle through magnetic field 110 would cause a changerecognizable by two or more magnetic field sensors 220 a and 220 b inone or more magnetic field monitors 260. By comparing the strengths ofsignal 130 or output signals 250 for each of magnetic field sensors 220a and 220 b, a location, direction, speed of travel, or the like for theperson carrying the rifle may be provided. Moreover, by networking aplurality of magnetic field monitors 260, a much larger area may bemonitored. For example, the magnetic field monitors 260 may be laid outin a web type pattern, over a large distance with overlapping fields,over a large distance without overlapping fields, in a corridormonitoring fashion such as corridor 800, and the like.

In one embodiment, magnetic field monitor 260 is powered by means of anelectrical power source. This electrical power source may comprise aninternal power source, such as a system battery 815 as shown in FIG. 8,or an external power source, such as a transmission line that deliversalternating current and that may be accessed through an electrical wallsocket. Further, the sensor described herein may be small and portable,e.g., reduced power requirements possibly having a shorter range; largervehicle deployed, e.g., increased power requirements, thereby increasingthe range; or may be hard mounted, such as on or in a building or otherstructure. In one embodiment, magnetic field monitor 260 may beselectively powered up and selectively powered-down to extend batterylife.

Magnetic field monitor 260 may also be expanded to include data storagefor various purposes. For instance, in an embodiment, signal 130,relative baseline signal 280 and/or information generated by instantcomparator 210 and block comparator 230 is stored in a storage unit suchthat the data may be subsequently retrieved and further processed. Forexample, a hard disk drive (HDD) or random access memory (RAM) is usedto electronically store the data by means of arrays of electroniccapacitors that are configured to acquire an electronic charge, whereinthe charging of the capacitor arrays corresponds to a digitalrepresentation of the acquired data. However, it is understood that theaforementioned examples are merely exemplary of different storage unitsthat may be implemented pursuant to various embodiments of the presenttechnology. Other suitable storage units may also be utilized to storedata such that it may be later accessed and processed. For instance, aportable flash drive may be used to store data, and the flash drivecould be physically transported from a first computing system to asecond computing system, wherein both computing systems are capable ofaccessing data stored on the drive.

Example Computing System

Referring now to FIG. 7, a diagram of computer system 700 in accordancewith one embodiment of the present invention is shown in greater detail.Within the discussions certain processes are discussed that arerealized, in one embodiment, as a series of instructions that residewithin computer readable memory units of system 700 and executed byprocessor 702 of system 700. When executed, the instructions cause thecomputer system 700 to perform specific functions and exhibit specificbehavior as described.

In general, computer system 700 used by the embodiments of the presentinvention comprises an address/data bus 701 for communicatinginformation, one or more central processors 702 coupled with the bus 701for processing information and instructions, a computer readablevolatile memory unit 703 (e.g., random access memory, static RAM,dynamic, RAM, etc.) coupled with the bus 701 for storing information andinstructions for the central processor(s) 702, a computer readablenon-volatile memory unit 704 (e.g., read only memory, programmable ROM,flash memory, EPROM, EEPROM, etc.) coupled with the bus 701 for storingstatic information and instructions for the processor(s) 702.

System 700 also includes a mass storage computer readable data storagedevice 705 such as a magnetic or optical disk and disk drive coupledwith the bus 701 for storing information and instructions. Optionally,system 700 can include a display device 706 coupled to the bus 701 fordisplaying information to the computer user (e.g., maintenancetechnician, etc.), an alphanumeric input device 707 includingalphanumeric and function keys coupled to the bus 701 for communicatinginformation and command selections to the central processor(s) 702, acursor control device 708 coupled to the bus for communicating userinput information and command selections to the central processor(s)702, and a signal generating input/output device 709 coupled to the bus701 for communicating command selections to the processor(s) 702.

Examples of well known computing systems, environments, andconfigurations that may be suitable for use with the present technologyinclude, but are not limited to, personal computers, server computers,hand-held or laptop devices, multiprocessor systems,microprocessor-based systems, set-top boxes, programmable consumerelectronics, network PCs, minicomputers, mainframe computers,distributed computing environments that include any of the above systemsor devices, and the like.

It should be further understood that the examples and embodimentspertaining to the systems and methods disclosed herein are not meant tolimit the possible implementations of the present technology. Further,although the subject matter has been described in a language specific tostructural features and/or methodological acts, it is to be understoodthat the subject matter defined in the appended claims is notnecessarily limited to the specific features or acts described above.Rather, the specific features and acts described above are disclosed asexample forms of implementing the claims.

What is claimed is:
 1. A method for monitoring an area of interest witha plurality of magnetic field sensors, said method comprising: providinga first magnetic field sensor on a first side of an area to bemonitored; providing a second magnetic field sensor on a second side ofthe area to be monitored, a location of the first magnetic field sensorand the second magnetic field sensor resulting in an overlapping area tobe monitored; receiving a first magnetic field strength signalintermittently from the first magnetic field sensor at a magnetic fieldmonitor; receiving a second magnetic field strength signalintermittently for the second magnetic field sensor at said magneticfield monitor; comparing, at said magnetic field monitor, said firstmagnetic field strength and said second magnetic field strength for agiven time period; determining, at said magnetic field monitor, whethera change in either of said first or said second magnetic field strengthis correlated with a change in the other of said first or said secondmagnetic field strength, wherein a correlated change would signify anevent occurring in an overlapping area; providing no output signal if itis determined that the event was not occurring in said overlapping area;and generating an output signal from the magnetic field monitor if thechange in the magnetic field strength in the overlapping area is greaterthan or equal to a pre-defined threshold.
 2. The method of claim 1,further comprising: providing an imaging device to capture imagery ofthe overlapping area; and initiating the imaging device to captureimagery when the output signal is generated.
 3. The method of claim 1,further comprising: utilizing an internal power source to power themagnetic field monitor.
 4. The method of claim 1, further comprising:utilizing an external power source to power the magnetic field monitor.5. A magnetic field corridor monitor comprising: a first magnetic fieldsensor on a first side of a corridor to be monitored; a second magneticfield sensor on a second side of the corridor to be monitored; and amagnetic field monitor to receive a first and a second magnetic fieldstrength signal for the corridor from the first magnetic field sensorand the second magnetic field sensor respectively, compare said firstmagnetic field strength and said second magnetic field strength for agiven time period; determine whether a change in either of said first orsaid second magnetic field strength is correlated with a change in theother of said first or said second magnetic field strength, wherein acorrelated change would signify an event occurred in the corridor;provide no output signal if it is determined that the event had notoccurred in said corridor; and provide an output signal when the changein the magnetic field strength in the corridor is greater than or equalto a pre-defined threshold.
 6. The magnetic field corridor monitor ofclaim 5, further comprising: an imaging device to capture imagery of thecorridor wherein the imaging device is activated when the output signalis generated.
 7. The magnetic field corridor monitor of claim 5, furthercomprising: an internal power source to power the magnetic fieldmonitor.